1. Field of the Invention
The present invention relates to a technique which captures information on texture of an original and reproduces the information in an image reader.
2. Description of the Related Art
Surfaces of objects respectively have “textures”. For example, a surface of polished metal gives “glossiness” to a viewer, while a surface of cloth or a fabric gives glossless “matte feeling” to a viewer. To express an object with more reality like an actual object, it is necessary to capture information on texture (texture information) such as gloss and feeling (external appearance and touch) of the actual object and reproduces the texture information. Accordingly, in an image reader of a scanner, a copying machine or the like, an attempt has been made to read not only the color information of an object but also the texture information of the object.
The texture of the object depends mainly on a reflection condition of light on a surface of the object. In general, the reflection light on the surface of the object is composed of a specular reflection light (or mirror reflection light) having high directivity and a diffuse reflection light having low directivity, wherein the texture of the object differs depending on a ratio between these lights. For example, the ratio of the specular reflection light is relatively high on the surface of the polished metal and hence, the glossiness is imparted to the surface of the metal. On the other hand, on the surface of the glossless object such as cloth or fabric, the ratio of the diffuse reflection light is relatively high. That is, the acquisition of ratio between the specular reflection light and the diffuse reflection light by measuring the reflection light from the surface of the object leads to the faithful expression of the texture of the object, more particularly, the degree of gloss level.
In the image reader, the object which constitutes an original is read using the diffuse reflection light. That is, in the image reader, the reflection light containing a large amount of diffuse reflection light from the original is received, and color information of the object is generated based on the diffuse reflection light. On the other hand, when the image reader is configured such that the reflection light which contains a large amount of specular reflection light from the original is received, there may be a case in which the specular reflection light component becomes excessively large depending on a surface condition of the original and the color reading performance of the original image based on the diffuse reflection light is lowered. Accordingly, an imaging optical system is designed such that the specular reflection light from the original is minimized so that the reflection light containing the diffuse reflection light as much as possible is received.
On the other hand, to read the texture of the surface of the original, the image reader may be configured such that both of the diffuse reflection light and the specular reflection light from the original are received, and the color information and the texture information are obtained based on the respective reflection light components. For example, a technique has been known in which an image mainly containing the diffuse reflection light (the diffuse reflection image) is read by light emitted from a light source to an object to be copied (original), an image mainly containing the specular reflection light (mirror-surface reflection image) is read by light emitted from another light source to the object to be copied, and a gloss signal which indicates the gloss is generated based on these image signals. That is, in this technique, color information of the object to be copied is obtained based on the diffuse reflection light, and the texture information of the object to be copied is obtained based on the specular reflection light.
However, the acquisition of texture information of the surface of the original using this technique gives rise to the following drawbacks.
In the above technique, the optical system contains two different illumination units, an illumination unit (light source) for obtaining the diffuse reflection light and another illumination unit (light source) for obtaining the specular reflection light. Accordingly, the configuration for illuminating the original becomes large-sized and pushes up a cost. Further, these illumination units take different reading positions and hence, in overlapping images obtained by the reflection lights, that is, in overlapping the diffuse reflection image and the specular reflection image, it is necessary to correct the position of image signals using a memory or the like corresponding to the shifted positions of the diffuse reflection image and the specular reflection image.
Further, in the above-mentioned configuration, since an optical path length of the reflection light for reading the diffuse reflection light and an optical path length of the reflection light for reading the specular reflection light are not the same and hence, unless any measures are taken, at least one reflection light is received without being properly focused as an image. Accordingly, to allow the reflection lights to perform the proper imaging, it is necessary to perform the adjustment of focusing points of the reflection lights each time, and to perform the reading operation of the original twice.